As an organic compound having a sulfo group (—SO3H), a fluorinated polymer having sulfo groups, and a fluorinated organic compound having a sulfo group excluding a fluorinated polymer have been known.
A fluorinated polymer having sulfo groups and its derivative are used e.g. as an electrolyte membrane of a polymer electrolyte fuel cell or an ion exchange resin covering catalyst fine particles (such as metal-supported carbon black) in a catalyst layer of a polymer electrolyte fuel cell. Further, a fluorinated polymer having sulfo groups and its derivative are used as a liquid composition as dispersed or dissolved in a medium containing water. Such a liquid composition is used as a material to form an electrolyte membrane or a catalyst layer of a polymer electrolyte fuel cell.
A fluorinated organic compound having a sulfo group excluding a fluorinated polymer is used e.g. as an electrolytic solution of a lithium ion battery or an additive for the electrolytic solution after conversion into a lithium salt.
As a method for producing an organic compound having a sulfo group, for example, the following method has been proposed.
(1) A method comprising a step of subjecting a compound having a fluorosulfonyl group (—SO2F) to alkali hydrolysis treatment in an alkali solution containing an organic solvent and water to convert the fluorosulfonyl group to a sulfonate type functional group (—SO3M, wherein M is an alkali metal), and a step of subjecting the compound having the sulfonate type functional group to acid treatment to convert the sulfonate type functional group into a sulfo group (Patent Documents 1 to 3, Non-Patent Document 1).
As a method for producing a liquid composition, for example, the following method has been proposed.
(2) A method of heating a fluorinated polymer having sulfo groups or its derivative in a medium, with stirring and mixing (Patent Document 3).